1. Field of the Invention
This invention relates to fastening devices and more particularly it concerns novel tack-like fastening devices which are highly resistant to unauthorized release by fracturing or the like.
2. Description of the Prior Art
U.S. Pat. No. 3,628,267 to A. J. Minasy and U.S. Pat. No. 3,858,280 to M. A. J. Martins show tack-like fastening devices used to hold a plastic wafer to an article of merchandise. The plastic wafer serves, externally, as a label on which price, size, etc., pertaining to the merchandise may be printed. Inside the wafer, however, there is embedded an electronic circuit; and if the merchandise is taken through a door or other specially wired exit the electronic circuit in the wafer will cause an alarm to be sounded. A system suitable for providing this alarm is described in U.S. Pat. No. 3,500,373 to A. J. Minasy.
It is important that the wafer fastening device be capable of holding the wafer securely to the merchandise and that it be highly resistant to release in an unauthorized manner. It is also important that the fastening device does not harm the merchandise. In general, the fastening devices employed to secure wafers to articles of merchandise comprise a tack-like element having an expansive, generally flat, head with a thin pointed shank extending out from the center of one side of the head. The shank pierces the merchandise and passes through a small opening in the wafer. It then enters a button-like fastening element and becomes locked therein by some means which can be released only by a special device at a checkout counter or authorization station.
One technique that has been used in the past to remove wafers from articles of merchandise without authorization is to exert sharp pulling forces between the merchandise material and the wafer to pull up on one side of the tack head and bend its shank. If this pulling is done in a particular manner it may be possible to bend the shank sufficiently to sever it and thereby release the wafer from the merchandise.